Pinning characteristics in chemically modified (Nd, Eu, Gd)–Ba–Cu–O superconductors

Abstract

In melt-processed (Nd0.33Eu0.38Gd0.28)Ba2Cu3Oy (NEG-123) materials we found a new type of nanometer-scale pinning defects. Structural analysis was made with a dynamic force microscope and a scanning tunneling microscope (STM) that both showed the formation of a nanometer-scale lamellar structure. The high magnification STM showed that the nanolamellas are in fact rows (or planes) of aligned NEG-rich clusters 3–4 nm in size. This new pinning medium led to an increase of Birr at 77 K for the H∥ c axis up to 12 T (measured by a superconducting quantum interference device) or 15 T (measured by a vibrating sample magnetometer). A secondary peak as high as 70 kA/cm2 was observed at 4.5 T and decreased to 49 and 22 kA/cm2 at 7 and 10 T, respectively.